Decisions, Decisions, Decisions on which battery pack/ tech

[markcycle]

Not using a BMS with LI-Ion is a very dangerous thing. They weren't created for no reason.

My 120 cell LI-ION pack has 9 BMS circuits, and I'm glad they do. On top of that I have a current monitoring circuit I designed which alerts me when a pack is out of balance.

My system is three 37 volt 9AH battery packs in parallel Each pack is divided into 3 subpack in series. For a total of 37 votls and 27 AH

Now if any one of the series packs gets shorted then the BMS shuts down, also if the full 37 9AH pack shorts the BMS shuts the pack down. This can leave me running on 2 of the 3 parallel packs so then the current monitoring circuit alerts me of a imbalance between the 3 main parallel packs. I can keep going but I know there is a problem with one of the packs.

Also my monitor alerts me if I get a back charge from one pack to another. Since I'm not using didoes if one pack should have a higher voltage for some reason and turns on into the other two I get alerted. This can happen if a pack see a glitch shuts down then turns on sometime later into the other two pack which are at a lower voltage. Since my primary BMS circuits only shut down on over charge voltage and not charge current this potential hazard needs to be avoided or didoes used wasting power and 3 separate chargers.

Never run LI-ION on feel or if you do accept the consequences of having a fire under your ass and if your lucky just blown cells as Xyster has had happen.

Good luck

PS leave the battery building to those who have a understanding of electronics, electricity and electrical safety PLEASE A shorted battery has no off switch batteries have no off switch

Mark

[xyster]

BMS's regularly fail. BMS's provide reason not to check the cells individually, and make access to the pack for individual cell testing or replacement more difficult. BMS's may provide a sense of security, but it's a false sense of security. The LiMn or LiFePO4 cells BiGH is leaning towards don't need a BMS. Packs of these chemistries are often sold without a BMS.
http://bigerc.com/index.php?cPath=21&os ... 10e8bf17ce

A LVC provided by the CycleAnalyst, and occasional cell balancing with one or more individual chargers does most of the work of a BMS anyway.

BMS's protect the manufacturer and seller from liability and lost sales due to lithium safety concerns more than they protect the consumer.

A shorted battery has no off switch batteries have no off switch

The 18650s like I use have either a built in PTC fuse, or a built-in BMS called a PCB. So they do have an off switch and it does seem to work, though not always well enough to prevent permanent cell death when operating outside the spec'd limits.

[BiGH]

Not using a BMS with LI-Ion is a very dangerous thing. They weren't created for no reason.

My 120 cell LI-ION pack has 9 BMS circuits, and I'm glad they do. On top of that I have a current monitoring circuit I designed which alerts me when a pack is out of balance.

My system is three 37 volt 9AH battery packs in parallel Each pack is divided into 3 subpack in series. For a total of 37 votls and 27 AH

Now if any one of the series packs gets shorted then the BMS shuts down, also if the full 37 9AH pack shorts the BMS shuts the pack down. This can leave me running on 2 of the 3 parallel packs so then the current monitoring circuit alerts me of a imbalance between the 3 main parallel packs. I can keep going but I know there is a problem with one of the packs.

Also my monitor alerts me if I get a back charge from one pack to another. Since I'm not using didoes if one pack should have a higher voltage for some reason and turns on into the other two I get alerted. This can happen if a pack see a glitch shuts down then turns on sometime later into the other two pack which are at a lower voltage. Since my primary BMS circuits only shut down on over charge voltage and not charge current this potential hazard needs to be avoided or didoes used wasting power and 3 separate chargers.

Never run LI-ION on feel or if you do accept the consequences of having a fire under your ass and if your lucky just blown cells as Xyster has had happen.

Good luck

PS leave the battery building to those who have a understanding of electronics, electricity and electrical safety PLEASE A shorted battery has no off switch batteries have no off switch

Mark

What battery packs did you buy?

The problem i find with a lot of BMS's (or should that be BMS') is that they will fry at higher voltages. Knoxie has fried one. I'm looking at 72v+ operation and that tends to fry BMS' too.

I'm all for extra saftey, and would definately run packs that have a BMS if possible. I just want to weigh up all the options first.

Xyster isn't running a bms, and while it is less safe, it isn't necessarily bad. its just less safe!

i'm also finding an issue that there are not really any places in Australia that sell battery packs, or if they do they're not compeditive (solarbbq's packs are an exception - they are compeditive)

[Mark_A_W]

You are having the same struggle I had.

When I did find a pack locally I jumped on it.

Which pack can Brett source now?

When I asked he was in-between suppliers, and the only thing was the cartridge E-bike style ones, not very friendly to mount.


Oh, and how do you make a guess whether the BMS will take higher voltages with 2 batteries in series? Check the voltage values of the components?

I don't quite understand why the BMS cops double the voltage - can someone explain that?

Big H, if you end up making a pack, let me know. I might jump on board and make myself a ~12v 10Ah pack to turbo boost me to 48v (or more like 54-55v).

Mark

[markcycle]

What battery packs did you buy?

I got 3 Crystalyte 37 volts 9AH packs as my base

The problem i find with a lot of BMS's (or should that be BMS') is that they will fry at higher voltages. Knoxie has fried one. I'm looking at 72v+ operation and that tends to fry BMS' too.

Change the Fets go with a custom pack the fets in my pack are 60 volts. Yes they will blow at 72 volts. If I needed that voltage I would change the fets and make sure the Aux voltages (chip voltages) were going to be OK.

I'm all for extra saftey, and would definately run packs that have a BMS if possible. I just want to weigh up all the options first.

Xyster isn't running a bms, and while it is less safe, it isn't necessarily bad. its just less safe!

If he has a hard (welded) short it will be bad - could be bad very bad

i'm also finding an issue that there are not really any places in Australia that sell battery packs, or if they do they're not compeditive (solarbbq's packs are an exception - they are compeditive)

You get what you pay for

Mark

[xyster]

If he has a hard (welded) short it will be bad - could be bad very bad

With lithium cobalt, that could be very bad with or without a BMS. A BMS can't cut-off a cell from itself; can't help a cell that shorts on the inside, or before its connection to the BMS.

[Ypedal]

I have run my packs at 72v, no problems yet. Specify this when you order a pre-made pack.

[BiGH]

You are having the same struggle I had.

When I did find a pack locally I jumped on it.

which pack?

Which pack can Brett source now?

When I asked he was in-between suppliers, and the only thing was the cartridge E-bike style ones, not very friendly to mount.

Not sure on suppliers he's getting cells next week though

[Mark_A_W]

I got mine from ruggedmachinery on ebay.

It charges to 41v, it's 10ah (I think) and Lithium Manganese Sulphate (I think), and weighs 3.8kg.

Does at least 50k with pedalling, and runs 70w of lights with little or no performance drop as well.

You can see a pic of it in this thread:
http://endless-sphere.com/forums/viewtopic.php?t=1319

[xyster]

I got mine from ruggedmachinery on ebay.

It charges to 41v, it's 10ah (I think) and Lithium Manganese Sulphate (I think), and weighs 3.8kg.

Yah, uhmmm, good thing you've got an unidentified BMS with who-knows-what specs to protect that mysterious pack! All considering, it doesn't sound any less risky than my BMS-less pack of well-known, widely-used 18650s.

[Mark_A_W]

Yep...but's it's ok, I can get my backpack off in a hurry if it catches fire.

Well, it was either this battery, or 12kgs of SLA. Which would you choose?

[markcycle]

If he has a hard (welded) short it will be bad - could be bad very bad

With lithium cobalt, that could be very bad with or without a BMS. A BMS can't cut-off a cell from itself; can't help a cell that shorts on the inside, or before its connection to the BMS.

But then you got PTC protection as all LI-ION cells have. Can't make the risk zero, not trying to. Just doing the customary and expected for a design of this type.

In the engineering world thats what is expected by the courts and of course you are still endlessly hassled (Been there done that discovery, testimony the whole shin bang) ). But if you want your insurance company on your side, then you research what is required by CE and UL and whoever else and do it right and document it (my weakness).

Now why do I care, the battery is just for me.

So I can sleep at night

Well if I get into a accident and that battery goes up in flames due to a impact. I'm in deep shit first Ebikes are illegal in NY wait I need to phrase this right, not allowed on the roads as per the DOT.

So its going to be a long legal battle to defend myself no matter who's fault it is. But with my engineering background in powersystems - not batteries though. I sleep well at night knowing I'm doing the best I can and also can show getting a battery cheap was not my direct goal but obtaining a light weight long range battery was my goal.

Saying my goal was to build something cheap is not going to cut it in the real world. It doesn't cost that much to add say 100 dollars to a design and stand up and say I did what the battery industry expects of a battery of this design. What would it take to put what you feel is the LV cutoff and put it into a circuit that either alerts you as a alarm system or a real cut off. Same with over current, its just not that hard and its the right thing to do.

Now for the most important reason, it was just plain fun, reverse engineering the C packs, taking them apart looking up the IC's then putting them back together and have them still work. Then seeing what I think is the weakness in my parallel pack design and designing and testing a system to deal with that weakness. Poor front brake, used it as a poor man Dyno for hours dropping out packs on over current restating them seeing the reverse charge effect 300mv delta in my packs creates about 3 to 5 amps of reverse current, so its diodes or a well designed protection system and of course fuses also test with enough reverse current so the fuses blow at 2C.

And the thrill of working on a live system

I can't say this enough

There is no off switch on a battery cell, you get a cell into thermal runaway and there is no fuel rods to push in no cooling water to turn on at the last second. Throw it in sand and hope for the best.

SO I PLAN ON DOING MY BEST WHEN MAKING A BATTERY

This isn't my last battery project, I'm hooked and maybe by next spring I might have a battery to sell completely of my own design

[xyster]

Yep...but's it's ok, I can get my backpack off in a hurry if it catches fire.

Well, it was either this battery, or 12kgs of SLA. Which would you choose?

Oh your pack, of course. But not because I think it's any less likely to catch fire than my BMS-less boxes of 18650s. We know nothing about those cells besides they're lithium (the weight tells us that), and I've seen no other user reports regarding them. Have you?

I think markcycle overlooks all these other issues in his blanket statements regarding risk assessment of going BMS-less.

[markcycle]

I'm not judging you just telling you what I did thats all

I am encouraging others not to go down the BMS LESS route thats all

I'm not asking to be judged or followed so why do you need to know my cell type I'm not selling anything just thinking about it

I told you what I did I would have done it with any LI-ION chemistry What I did was LI-ION chemistry independent

Be it A123 cells or any high energy cell the industry expects a BMS circuit for good reasons with this class of battery

Thats all I'm saying.

And you could add a BMS system for under 100 dollars to your battery (under voltage/Overcurrent). Does 100 dollars make or brake buying a battery come on; over the life of the battery its in the noise.

[xyster]

I'm not asking to be judged or followed so why do you need to know my cell type I'm not selling anything just thinking about it

Unless you're also Mark_A_W, I don't recall asking your cell type. I'll just assume you're a <a href="http://en.wikipedia.org/wiki/Eukaryote" target="_blank">eukaryotic</a> life form, like the rest of us. If not, that's cool too.

And you could add a BMS system for under 100 dollars to your battery (under voltage/Overcurrent). Does 100 dollars make or brake buying a battery come on; over the life of the battery its in the noise.

A hundred dollars is a lot of money to me. And I've got a pretty good BMS already: a voltmeter for the pack voltage, a voltmeter I take readings from each subpack with, an ammeter, the current limit of the controller, a fuse, PTC's on each cell, and 20 chargers to balance each subpack each time I charge. That's my Battery Management System.

I don't see what an expensive all-in-one BMS is going to do for me. And neither have I seen any commercially available BMS units designed to pass 60 amps or more -- the future limit after I upgrade my controller with the better FETs. Do you know any good sources for $100 40-60 amp 96 volt BMS's?

[markcycle]

Again if your happy with what you got GREAT But when you say things and I quote "you can FEEL the low voltage point of the batteries" thats your statement made earlier. That what got me started down this thread, which has resulted in use going back and forth for no reason. Your happy COOL I'm not judging

FOR NEWBIE'S Please don't build a battery using LI-ION cells with out understanding the dangers.

IT IS EXPECTED THAT A LI_ION BATTERY HAVE AT A MINIMUM OF CIRCUITS TO MONITOR AND FEEDBACK TO THE USER THE STATE OF THE BATTERY FOR BOTH CHARGING AND DISCHARGING. NO USER OF LI-ION CHEMISTRY SHOULD USE "FEEL" AS A CRITERIA FOR THE STATE OF THE SYSTEM. SUCH A SYSTEM SHOULD HAVE THRESHOLDS FOR ALL MONITORED PARAMETERS AND ALERT THE USER AT A MINIMUM. CRITICAL THRESHOLDS, IF THE TECHNOLOGY ALLOWS, SHOULD SHUT THE SYSTEM DOWN.

Do you know what a LM339 is? It's a 20 cents comparator, been around forever. You could build a monitoring BMS system using this chip and a few others. A little wire wrapping some knowledge, easily learned and you got a basic BMS system. thresholds can be set by adjusting a potentiometer as a reference. A few LED's on the handlebars and for next to nothing you got electronic monitoring of your battery. If You want to shut it down that is more complicated but doable after all your controller can switch the battery current. There was a thread here where a person was building his own BMS and setting thresholds to trip a circuit breaker, its doable for cheap.

Again I don't care what you do if your happy I'm happy but please don't relay how you feel the Low Voltage point of your system. As this may encourage some NewBe to hurt them self or worse.

[xyster]

Again I don't care what you do if your happy I'm happy but please don't relay how you feel the Low Voltage point of your system. As this may encourage some NewBe to hurt them self or worse.

B.S. When provided all the info and all sides of an argument, most people are very good at weighing the evidence and making up their own minds regarding decisions personally and directly affecting them. And those who aren't, will have far more serious problems in other areas of life.

The BMS's in cell phones and laptops obviously haven't prevented all those fires. A faulty BMS can be the source of dangerous problems too; provides a false sense of security; makes accessing and replacing cells more difficult; and is a measure to protect the manufacturer and vendor more than the consumer.

I haven't asked you to censor your opinion, why do you insist I censor mine?

[BiGH]

firstly i'm in australia so i need chargers that support 240v (which pretty much eliminates the dewalt donor idea.

Are there adapters of sufficient wattage available?

I visited total tools today and had a chat to the guys there. You can buy 36v Lithium dewalt cells and chargers in Australia.!!!!

for the "cheap" price of:
Battery: DC9360-xe Battery - $379AUD
Charger: DC9000-xe Charger $239AUD
(both prices include GST)

works out to be about double the price of buying the batteries in the states! but at least i know i can get Australian chargers...